[Heathkit] SB-10 Modification (was DX-100B on Phone - bad audio distortion / oscillation)

[Rick Poole]

Received in private email:

 >>>>>
>It would seem to be possible to remove them temporarily  (or at 
>least until you get hold of this problem) without forever nuking the 
>capability ...by removing the wires at the switch end.
<<<<<

I can always put it back if I want to, but there are wires that run 
the entire length and depth of the transmitter picking up all manner 
of who-knows-what along the way.

Apparently the combination of DX-100B and SB-10 is rare (the 
TX-1/SB-10 is much more common), as evidenced by the fact that I've 
asked a couple of times on these reflectors and haven't yet found 
anyone who has or has had that combination.  So I don't know for a 
fact that it ever really did work all that well in all of its modes.

 >>>>>
>Also, have you made sure the tank coil and associated connections 
>are solid and unmodified? I've seen that cause similar problems in an amp.
<<<<<

I have gone over everything in the PA section, except the parasitic 
suppressors and the screen bypass caps.

Part of the SB-10 mod is that the connection between the driver and 
the finals, originally about a 2-inch route through a bulkhead 
feedthrough, now goes from the driver, all the way to the farthest 
corner of the transmitter and out a coax connector, through an 
external jumper to another coax connector, and thence to the grids of 
the final tubes.  Normally the SB-10 connects where the external coax 
jumper is.  Seems to me that, even though (very LARGE) shielded coax 
was used from the output of the driver to the coax connector at the 
far corner, still there is plenty of opportunity to pick up unwanted 
stuff.  So, that'll be the first thing I reverse to see if it makes a 
difference.